Variability of inorganic nutrients in the Western Mediterranean Sea

Abstract

The Mediterranean Sea is considered as a complex marine ecosystem because of its changes and the variety of the regional physical processes occurring in the area such as the thermohaline circulation, vertical mixing and deep-water formation. One of the major challenges in ocean monitoring is to understand and estimate the changes in chemical and biogeochemical properties of seawater, since they might be affected by various processes. The Mediterranean Sea is characterized by various nitrate to phosphate ratios due to the overall circulation and atmospheric and terrestrial inputs The purpose of the PhD project was focused on inorganic nutrient variability in the Western Mediterranean Sea. Thus, to investigate spatial and temporal changes in biogeochemical properties on the Western Mediterranean Sea throughout the 2004-2017 period. It is mainly based on the in-situ observation collected during various European projects, a regional comparison of biogeochemical properties at regional scale and on a climatological study at the scale of the integrality of the Western Mediterranean. We performed a careful primary and secondary quality control of nitrate, phosphate and silicate measurements and generated a new product (CNR_DIN_WMED) with unpublished oceanographic data in the Mediterranean Sea. Since there are still monitoring gaps, both in time and in space related to nutrient observations, the new data product provides a good spatial and temporal coverage. We compared biogeochemical properties between regions of the WMED, and set an inventory of average ratio characterizing each region, trying to relate the effect of the local physical mechanisms. In the final part, a climatological analysis on the WMED was embedded to quantify and investigate the spatial and temporal variability of nutrients at different depth levels. The WMED is turning to a relatively nutrient enriched basin after the Western Mediterranean transient at intermediate and deep layers.